OVER the past 15 years war in the Democratic Republic of Congo has consumed as many as 5m lives, often gruesomely: children murdering in gangs, civilians massacred by the thousand, rape as common as petty thievery. And yet, who can name the man responsible?

The fact that the war is so recent adds to the confusion; splinter conflicts continue. Time is not only a healer but also a revealer and crystalliser of atrocities. Only with the trial of Adolf Eichmann in 1961 did the term “Holocaust” become common currency for Germany's extermination of the Jews in the second world war. The complexity of the conflict in Congo further obscures its significance. It has no Stalingrad, no Stalin. Murder there has been systemic rather than systematic in the manner of the killings at Auschwitz. Death has been abundant, though often with no clear perpetrator; many of the deaths have been as a result of war-wrought diseases.

Despite at one time having the world's biggest UN peacekeeping mission, Congo, Jason Stearns argues, should be ranked alongside Germany, Russia and China as one of the great vortexes of recent human violence. The conflict sucked in armies from nine nations, spawning at least 20 rebel groups that fought 40 or 50 interlocking wars within wars in a country as big as western Europe, but with few roads. Ethnic rivalry, lust for power, security concerns, poverty and greed all played a role, yet no side had a clear objective.

The 1994 genocide in next-door Rwanda lit a fuse in Congo. In 1996 a rebel army from eastern Congo marched a thousand miles across the lush country to depose Mobutu Sese Seko—he of the leopard skin fez—whose regime had been badly weakened by the winding down of Western support after the cold war. Arriving in Kinshasa, the capital, the rebels' leader, Laurent Kabila, admonished the crowds, “Who has not been Mobutist in this country? We saw you all dancing in the glory of the monster.”

Tens of thousands of refugees had been killed in his journey west; in that sense Kabila was no better than his predecessor. He also jailed opponents and turned the treasury into his personal piggy bank, sometimes with bizarre results. When an official visitor asked for directions to the toilet at Kabila's residence, a guard nervously searched for the key to a locked en-suite bathroom. Eventually the visitor was led to another building to relieve himself, while Kabila admonished the guard, “You idiot! I had the key the whole time! All my money is stored in that toilet.”

The state crumbled further under Kabila's rule, and rebellion followed rebellion until he was shot by one of his own former child soldiers in 2001. His son took over, managing eventually to contain the conflict in the east of the country, where it continues to fester, fed by hunger for the area's abundant mineral deposits and by the presence of rival outsiders, notably its Rwandan neighbours. Mr Stearns, an American former journalist and UN worker who has spent a decade following the conflict, speaks many of the local languages and has a knack for loosening tongues. He is at his best when exploring the role that Rwanda has played in the war.

It is tempting to see the conflicts in both countries as essentially one. In the early 1990s ethnic Tutsi rebels from both sides of the border had fought the Hutu-led Rwandan government, which was supported by Mobutu. After the Rwandan genocide many of the Hutu perpetrators fled to eastern Congo, where they regrouped. To stop them, Rwandan Tutsis recruited Kabila, an ageing revolutionary, and engineered his rise. When he eventually turned against them, they found new proxies and in 1998 invaded themselves, driven by fear of the génocidaires, a lust for revenge and a growing appetite for diamonds. This launched the first Congo war.

Can this explain the appalling brutality of the conflict? Half a million women raped, some young girls of only five raped with gunbarrels or sticks, pregnant women disembowelled. Mr Stearns has met men who routinely killed 100 people a day, “using a rope to crush their windpipes and strangle them”. He asks how you become a mass murderer and finds unthinking machismo and delirium from years of abuse, but also strategic considerations. He seeks “a rational explanation for a truly chaotic conflict” and refuses to fall back on easy answers like the wanton savagery of Joseph Conrad's “Heart of Darkness”. “The killers wanted to show the villagers…the consequence of any resistance. There were no limits to their revenge—they would kill the priests, rape the nuns, rip babies from their mothers' wombs, and twist the corpses into origami figures.”

Mr Stearns enriches his narrative with portraits of the main actors—men such as Kabila's son and successor, Joseph, who panicked at the sound of gunfire—and an array of personal anecdotes. When Mobutu, shortly before his fall and riddled with cancer, ordered the printing of yet another new banknote to try and combat chronic inflation, it was dubbed “The Prostate” since the zeroes expanded as quickly as the leader's gland. After the fall Kabila's men found a single French 50-franc note in the central bank, left behind “as an insult”. Mr Stearns is not a scholar of central Africa in the manner of René Lemarchand and Gérard Prunier. But he is probably the most widely travelled and the most meticulous and empathetic observer of the war there. This is a serious book about the social and political forces behind one of the most violent clashes of modern times—as well as a damn good read.

Correction: Rwandan Tutsis invaded Congo in 1998, launching the first Congo war, not 1996 as we originally wrote. This was corrected on May 4th 2011.